This invention is based on a method for detecting optical radiation such as laser radiation in at least one defined sectional area of a protective housing, whereby the optical radiation is detected by a receiver supplied with a reference radiation emitted by a transmitter. The invention is also based on an arrangement for detecting penetration of optical radiation, particularly continuously or pulsed laser radiation in a sectional area limited by at least one of two walls of a housing of a protective wall system in which at least one receiver is located for detection of the radiation and this receiver is connected to an evaluation circuit.
State-of-the-art high performance lasers are used for processing material in industrial production. Portal systems and robot systems provide users with maximum flexibility for guiding the laser beam in relation to the work. If it is possible to guide the laser energy to the processing location using fiber optic cable, it would be possible to significantly improve the dynamics of such systems. For safety of life and limb, passive (absorbing) protective walls, usually of metal, are constructed using single plates or a number of plates located behind one another around the laser area, the so-called housing. Laser radiation occurs with extremely high energy density within these protective walls.
Processing of parts also results in uncontrolled reflections. Direct or indirect laser radiation, in the worst case, the untreated beam, strikes the housing, which has the purpose of providing protection to humans outside against such radiation. It is necessary to ensure this protection for a period of time t, depending on the operating mode of the laser system, i.e. to allow the user time to recognize the fault and shut down the system. Due to the high laser energy and the frequently low distances to the protective wall, this period of time t until shut off is decreased continuously, or the material requirements placed on the housing increase continuously. For this reason, walls with exclusively passive effect are only suitable for protecting humans to a limited extent.
Patent publications DE 100 17 284 C1, DE 103 25 906 A1, DE 196 29 037 C1 are based on purely passive protection by different versions of certain characteristics and intermediate spaces between the walls. Various heat conduction properties or reflection capabilities are utilized for realization of such passive radiation safety. In practice, however, the surfaces of the protective walls are contaminated by oil, dirt and dust within a short time to such an extent that the original properties of the protective devices are no longer present.
DE 36 38 874 C2 describes an active process, whereby the inner wall facing the laser is equipped with an electrically active conductor, similar to a melting type fuse. In comparison to the arrangement described here, safe function is ensured only when the absorption characteristics of the inner wall are matched exactly to the wave length of the laser and an electrically active safety feature is also included. In order to use this system for items such as fiber lasers with extremely small beam diameter, it would be necessary to embed the electrical conductor in the wall in a very close meandering pattern which would result in high design requirements and costs.
DE 89 08 806 U describes an arrangement nearly identical to that described above.
DE 199 40 476 A1 describes an active arrangement for recognition of optical radiation by means of a type of sensor. However, in this process, the design of the protective wall is a significant part of the function. The use of heat sensors on a wall facing the laser requires a significant number of sensors for reliable switch-off, depending on the heat conducting characteristics of the wall material. The version described equipped with optical sensors and a perforated sheet metal wall equipped with a foil on the inside requires specially designed wall elements for its part.
An arrangement, as well as method for detecting a laser beam which escapes from a working area, are known from EP-B-0 321 965. Here, the working area is surrounded by a wall, in which a detector is located, with which the illumination is measured, which is generated by the laser beam as it strikes the wall. To check the sensor, the surrounding housing has a cutout in which a photo emitter is located whose radiation is received by the receiver for checking the function of the latter.
A safety system for checking laser beams is described in GB-A-2 171 513. Here, the laser beam is detected by means of a receiver. An infrared light source, whose radiation is detected by the receiver, is provided for checking the functional capability of the receiver.